A radio access network (RAN) typically includes base transceiver stations (BTSs), each of which radiate to define one or more wireless coverage areas. In each coverage area, the RAN may transmit on a plurality of channels, each channel defined by a frequency. For each channel in the plurality of channels, the RAN may transmit on a plurality of subcarriers within the channel. For example, the RAN may use orthogonal frequency-division multiplexing (OFDM) to transmit on multiple subcarriers within a channel. OFDM is used in wireless communication systems such as IEEE 802.11 (WiFi) systems, IEEE 802.16 (WiMAX) systems, and systems that use the Long Term Evolution (LTE) specifications of the 3rd Generation Partnership Project (3GPP).
In the OFDM approach, data is organized into symbols that are used to modulate a plurality of sub-carriers. The sub-carriers are spaced apart in frequency by a subcarrier spacing, Δf. Each subcarrier in the channel may define a sequence of frames, with each frame having a duration of T. Further, each frame may be divided into a sequence of time slots, with each time slot having a duration of t. Within each time slot, the symbols containing data may be transmitted in parallel on the subcarriers. Additionally, the RAN may transmit symbols at a nominal power level in each of a plurality of the time slots.
Each wireless communication device (WCD) may use one or more channels in the plurality of channels for the transmission of voice and data. For example, a WCD may simultaneously transmit voice on a first channel and data on a second channel. Additionally, the WCD may transmit data on several channels at once to maximize data throughput. The RAN may assign one or more channels to each WCD based on network capacity, RF channel conditions, or data throughput needs. Furthermore, channel assignments associated with the various WCDs in a coverage area may change with every subsequent frame.